In the process of loading volatile liquid products into a vessel, such as for transport, volatile liquid vapor is produced. Venting such vapor into the atmosphere is problematic both from an environmental perspective, and because valuable product is lost in the process. For example, a typical loading facility's air permit may be limited to 50 tons per year of volatile organic compounds (VOCs). By loading a single 200 barrel truck each day and venting the gases into the atmosphere, 14.8 tons of the 50 ton annual limit will be exhausted. Accordingly, volatile liquid vapor recovery systems have been used to remove and recover the volatile liquid vapor.
Another consideration in the loading and recovery process is that an empty tanker truck or railcar includes a relatively large volume of air. About 21% of that air is oxygen. When a tanker truck is filled with a volatile liquid product, that air is displaced into the volatile liquid vapor recovery system normally utilized to collect the volatile liquid vapor produced during the filling or loading process. That system traps volatile liquid vapors which are absorbed by a bed of adsorbent and vents much of the “clean” air to the atmosphere.
However, in a conventional recovery system, air, including oxygen, is maintained in the overhead space of the reaction vessel containing the bed of adsorbent and in the lines leading to the vent. This can be problematic, as loading facilities generally have limits regarding the amount of oxygen that may be present. For example, a natural gas facility is typically limited to 10 ppm per ft3 of oxygen in the natural gas sales pipe line. When vapor balancing a 200 barrel load to a storage tank in order to reduce emissions, the process will inject on average 16 ft3 per minute of a 124,000 ppm O2 gas for a one hour period. Conventional vapor recovery systems are not equipped to both remove the oxygen from the recovery system and to return oxygen free (or significantly oxygen reduced) recovered volatile liquid vapor to a storage tank.
Accordingly, the present invention addresses the need to efficiently remove oxygen from a volatile liquid vapor recovery system.